1. Field of the Invention
The present invention relates to an electronic control unit having a connector electrically connecting the unit to outside devices and a circuit board on which driving elements and control elements are mounted, and more particularly to such an electronic control unit in which the connector and the circuit board are connected to each other through flexible wires.
2. Description of Related Art
Electronic control units for controlling operation of outside devices based on signals fed to and processed in the control units are generally known. An example of such electronic control units is briefly shown in FIGS. 17A and 17B (FIG. 17A shows an cross-sectional view, and FIG. 17B shows a plan view with an upper plate removed). In this example, a circuit board 40, on which various components such as control elements 53, driving elements 55 and passive elements 57 are mounted, and a connector 51 connecting the control unit to outside devices such as actuators and sensors are contained in a casing consisting of an upper case 50a and a lower case 50b. A plurality of connector pins 51a are inserted into through-holes 40a of the circuit board 40 and electrically connected to the circuit board 40.
Another example of conventional electronic control units for use in an automobile vehicle is briefly shown in FIG. 18. In this example, a circuit board 930 and a connector 935 are contained in a casing 938, and the connector pins 935a are inserted into the circuit board 930 and electrically connected thereto. An I/O circuit 934 having components 936, an ECT control circuit 932 for electronically controlling a transmission device, an ENG control circuit 933 having components 937 for controlling operation of an engine, and a throttle control circuit 931 for controlling operation of a throttle valve are all mounted on a single circuit board 930.
There are following problems in both types of conventional electronic control units. When the connector 51 or 935 is changed to another one in order to connect the control unit to different outside devices, an entire circuit board 40 or 930 has to be redesigned even if its function is not changed, because the connector pins are inserted into the circuit board having a circuit pattern printed thereon. The number of connector pins, the shape of the connector or the alignment of the connector pins have to be changed according to the outside devices to be connected to the control unit. In other words, plural circuit boards have to be prepared for matching various connectors even if the function of the circuit board is not changed. In addition, the size of the circuit board has to correspond to the size of the connector to accommodate the connector pins therein, even if a smaller circuit board is enough to cover a required function. In the conventional example shown in FIG. 18, which includes several control circuits in a single circuit board 930, an entire circuit board must be redesigned to change one of the control functions. All of the foregoing situations result in a higher cost in manufacturing the control unit.
The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an improved electronic control unit in which the design of the circuit board is standardized and simplified. Another object of the present invention is to provide an improved manufacturing method of such an electronic control unit.
The electronic control unit of the present invention is used for controlling operation of various devices. For example, the control unit is mounted on an automobile to control operation of an engine, a transmission device, a throttle valve and other devices. The electronic control unit is composed of a casing, a circuit board on which various electronic components such as transistors and microcomputers are mounted, a connector for electrically connecting the control unit to outside devices and flexible wires such as a flexible printed-circuit sheet connecting the connector and the circuit board. All those components are contained in a single casing. Various signals fed to the control unit from outside devices including sensors are processed in the control unit, and outputs for controlling the outside devices are generated in the control unit based on the processed signals.
The connector and the circuit board are not directly connected but are indirectly connected through the flexible printed-circuit sheet. Accordingly, if the connector is replaced with another type to match outside devices, it is not necessary to redesign the entire circuit board. Further, the casing is designed to be able to mount thereon variously sized circuit boards. Therefore, a circuit board having a desired function is selectively mounted on the same casing. For this purpose, surfaces for supporting variously sized circuit boards may be formed in the casing, or the supporting surfaces may be formed in steps so that each step can support a differently sized circuit board. Further, heat-generating components such as power transistors mounted on the circuit board may be disposed in the casing in contact with a heat-dissipation wall formed in the casing to quickly dissipate the generated heat.
The electronic control unit is assembled in the following manner. First, the circuit board carrying various components thereon and the connector are respectively mounted on the casing. Then, the connector and the circuit board are electrically connected through the flexible printed-circuit sheet. Preferably, one end of the flexible printed-circuit sheet is soldered to the connector before the connector is mounted on the casing, and then the other end of the flexible sheet is soldered to the circuit board after the connector is mounted on the casing. The other end of the flexible sheet is soldered to the circuit board, preferably, at a position where the circuit board is supported by the casing to avoid deformation of the circuit board. Thus, the control unit is efficiently assembled in a simple manner.
The circuit board may be divided into several circuit boards, each corresponding to a respective object to be controlled, e.g., a transmission device, an engine and a throttle valve. Alternatively, the circuit board may be divided into several circuit boards by function, e.g., a circuit board for handling input signals, a circuit board for processing signals and a circuit board for generating outputs. A certain number of variations for each functionally divided circuit board are prepared to cover various requirements, and circuit. boards meeting a particular requirement are selectively mounted on the casing. In this manner, control units meeting a variety of requirements are efficiently manufactured without making major changes in the entire unit.
A signal alignment board having a printed circuit pattern thereon may be interposed between the connector and the flexible sheet, so that the connector and the circuit board are electrically connected through the signal alignment board and the flexible sheet. Circuit crossovers in a circuit pattern formed in the flexible sheet are eliminated by using the signal alignment board. Further, noise-absorbing elements for eliminating noise fed into the control unit from outside may be mounted on the signal alignment board, thereby eliminating other noise-absorbing elements mounted on individual circuit boards.
According to the present invention, the design of the circuit board is standardized, and the electronic control units meeting a variety of requirements are efficiently manufactured at a low cost.
Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiments described below with reference to the following drawings.